This disclosure relates to managing ultraviolet (UV) radiation that a person is exposed to using a UV-measuring device. A system attempting to perform such measurements has previously been proposed [1]. It includes a wearable device that measures UV exposure and where the exposure data can be displayed to the user, either on the wearable device or on a remote mobile device (such as a smartphone or tablet) through a wireless transmission. Two important data are UV exposure and UV dose. UV exposure represents the instantaneous strength of UV radiation (usually in units of power or power per unit surface), while UV dose is the aggregated strength of UV radiation over a specified time period (usually in units of energy or energy per unit surface). One of the foundations of the exemplary system is the selection of a limit for UV dose that a user wishes to remain under over a specific period of time (usually during a day, which we will use thereafter but it could be an hour, a week, a month, etc.). In this disclosure, we describe several aspects or features of exemplary systems that provide guides to the user about setting this daily limit.
Why Would Users Measure their Exposure to UV Radiation?
Ultraviolet (“UV”) light is radiation in the wavelength range of 280-400 nm. Most of people receive their UV exposure from sunlight but some may be exposed to artificial UV exposure during their work (e.g. nurses) or for aesthetic purposes (e.g. tanning bed). UV exposure enables the skin to synthesize Vitamin D but overexposure to UV can cause adverse effects such as: skin redness, sunburn, systemic reactions in autoimmune diseases such as lupus, or pharmaceutical phototoxicity in the short term, and non-melanoma and melanoma skin cancer, skin aging, pharmaceutical photoallergy, photogenotoxicity, and photocarcinogenicity in the longer term (adverse effects thereafter).
Everyone has a Different Sensitivity to UV Exposure
Sensitivity to UV varies from person to person. Factors influencing UV sensitivity are comprised of genetic factors, history of UV exposure, concomitant medications, and medical conditions. For instance, on average, people with darker skin are more tolerant to UV exposure than people with fair skin. However, people with dark skin suffering from lupus are as sensitive, if not more, to UV exposure than people with fair skin. There is no way, a priori, to determine what daily UV dose a person can be exposed to without experiencing adverse events.
Lifestyle Greatly Influences how much UV Exposure a User Receives Everyday
On average, people living in tropics will receive a higher daily UV dose on average than people living in the middle latitudes because the UV exposure is higher, on average, in the tropics than in the middle latitudes. Similarly, people walking in direct sunlight will receive a higher UV dose than people walking in the shade in a nearby location.
Time spent outdoors varies from individual to individual. Outdoor runners spend more time outside during their exercise than indoor treadmill runners. Certain professions, such as construction, involve a longer time being outside on a daily basis, compared to office jobs for instance.
As result, the UV dose received by someone depends on both the UV strength and the time spent at the corresponding UV strength, two factors that heavily depend on someone's location and lifestyle.
Under such circumstances, the primary way to be able to control any adverse event caused by UV overexposure is to have an accurate knowledge of one's real-time UV dose and, as importantly, relate it to a limit that makes sense for this specific person so that she or he can avoid any adverse event by making sure her or his UV dose remains under this limit.
This is what is achieved by the proposed exemplary systems and methods, where the wearable device measures UV exposure and aggregates it to compute the UV dose, while the mobile device displays a UV dose limit to the user based on this information.
How to Measure Solar UV Exposure in a Way Relevant to Human Health?
In 1987, the human sensitivity to ultraviolet radiation was defined by Diffey and later adopted by the World Meteorological Organization and the World Health Organization [21]. This sensitivity is called the erythema action spectrum and gives exponentially more importance to high-energy photons. When measured on a horizontal surface, this standard metric is called the ultraviolet index (UV Index, or UVI). What impacts human health is the integration of UV exposure over time, referred to herein as the UV dose. When the UV exposure is weighted according to the erythema action spectrum, the accumulated dose is called the “erythemal dose”.
Typical UV measuring systems include a UV detector, which converts the incident ultraviolet radiation signal to electric current, coupled with additional circuitry. This includes an analog-to-digital converter (ADC), op-amp and microcontroller [1]. The current is then converted into a value for the UV index using a reference value of Some examples of these systems are the Solarmeter 6.5 UVI and the Genicom UV Index Meter. While such a system is capable of estimating the UVI, it is not accurate in a wide variety of situations because of the mismatch between their spectral sensitivity and the erythema spectrum [17, 20].
Why is it Important to Set a Personal Limit of UV Dose?
Every person has a certain UV dose they can tolerate in a given time span before it has an adverse effect. For some, depending on their location, this limit is small enough to be achieved in a few minutes to a few hours. If the UV dose limit is being approached, or has been exceeded, this information needs to be conveyed to the user so that he/she can act on it immediately. Otherwise it can lead to adverse effects. It is for instance known that UV exposure has a systemic impact on lupus and evidence shows that lupus patients experience more flares in the summer than in the winter [23]. Once a UV dose limit is set, a user may be notified when they have exceeded a certain percentage of that limit (e.g. 50%) by one of several methods e.g. a vibration, sound or light on either the UV sensor or the connected mobile device. There may be inventive aspects of this disclosure that do not rely on a real-time system. While real-time information has advantages that are called out herein, it is not necessarily an essential feature of every device, system, or method disclosed herein.
The state of the art in UV dosimetry recommends a UV dose based on skin type. These recommendations do not take into account the history of UV exposure, which influences the tolerance to UV dose, concomitant medications, and diseases. As a result, this method can lead to inappropriate UV dose limits for many users, and a result, lead to adverse events.